Nikki Kahn/The Washington Post(WASHINGTON) -- On the third anniversary of the day a U.S. government sub-contractor was jailed in Cuba for a project he was completing for the U.S. Agency for International Development (USAID), Washington again called for his release.

After serving three years of a 15-year sentence for what Cuban authorities call "Acts against the Independence or Territorial Integrity of the Cuban State," family members and the Obama administration are asking the Cuban government to let Maryland resident Alan Gross go.

"Mr. Gross is a 63-year-old husband, father, and dedicated professional with a long history of providing assistance and support to underserved communities in more than 50 countries," State Department deputy spokesman Mark Toner said in a statement released Monday.

When he was arrested, Gross was in Cuba working on a project for Development Alternatives, Inc., a company contracted by USAID, according to court documents.

Gross' wife filed a lawsuit on his behalf in November accusing DAI and USAID of failing to fully inform Gross of the risks associated with his tasks in Cuba, and failing to fully train him and supervise the selection process that got him the job. The couple is seeking $20 million in compensation from USAID.

Documents from the lawsuit against USAID say Gross was in Cuba to help "improve Internet access for the Jewish community in Cuba."

The United States has at least a moral responsibility to intervene on Gross' behalf, according to American University Professor Phillip Brenner.

"This work he was doing was on behalf of the United States. Whether they have a legal responsibility, I think the court has to decide that," Brenner said. "Whether they have an ethical -- a moral -- responsibility, there's no question that they do."

President Obama has been following Gross' case and requested that the Cuban government release him, White House Press Secretary Jay Carney said Monday at a press briefing.

"The Cuban government should release Alan Gross and return him to his family where he belongs," Carney said.

Appeals for Gross' release have focused on the humanitarian aspect of his imprisonment.

Rabbi David Shneyer visited Gross in fall 2011. In a newsletter to his congregation, Shneyer described how the Cuban jail officials, "created a comfortable space with two couches and a table with refreshments" for him to meet with Gross.

"I do know that Alan has lost a tremendous [amount] of weight," Shneyer wrote in an email.

Gross has lost more than 100 pounds in the last three years, a fact that Brenner said his wife points to as evidence he might have cancer. According to the Cuban government, Gross tested negative for cancer in October.

"I wish to inform you that a biopsy of the lesion that Mr. Gross has behind his right shoulder was performed on October 24 last, which confirmed that said lesion is not carcinogenic. The biopsy tested negative for neoplastic cells and it was confirmed that the lesion is made up by isolated muscle cells and extensive areas of red blood-cells that could be associated to a hematoma," José Ramón Cabañas, chief of the Cuban Interests Section in Washington, D.C., wrote in a letter dated Nov. 28, 2012 that was obtained by ABC News. "This test could not be performed before due to Mr. Gross's refusal."

Despite the Cuban official's assurances, Shneyer said, "There are still concerns about the lump on his shoulder."

In Monday's request from the State Department, Toner asked that the Cuban government, "grant Alan Gross's request to travel to the United States to visit his 90-year-old mother, Evelyn Gross, who is gravely ill," calling it a "humanitarian issue."

The letter from Cabañas included a summary of the U.S. case against a group of Cubans, known as the "Cuban Five," being held on espionage charges, about whom he said Cuba has "legitimate humanitarian concerns."